Bought my 4106 a couple years ago and was told by PO that it was upgraded to 318hp spec. I took this info with a grain of salt. Having read and become more knowledgable I now believe that 318hp should be n65 injectors with "A" timing.

Last summers we took the bus though 10 states and lots of altitude change. Max of over 8'000 MSL in Wyoming. I plan to do many more trips like this in the future.

The bus doesn't smoke @ sea level but as expected it does considerably and increasingly @ altitude.

So, my mind has begun to wander into the trap of performance upgrades...most notably a turbo, likely with a 8v71t swap. But common since has been prevailing and I had convinced myself that my bus most likely had stock injectors and not n65s because of the complete lack of black @ sea level. My mindset had become that I would upgrade the stock muffler (needs replacing anyways) with an upgraded Donaldson and perhaps upgrade to n65 injectors to see what I could get out of this 8v71 na motor before making a large upgrade.

Well, I had the valve covers off because my blower drive broke and I checked the injector size and was surprised to see that they are N70s. I don't know what to think about this. What's the deal with n70 injectors in an 8v71. My governor seems to be set @ 2450 with a load, v730, and 28,000lbs plus a 2,700 lbs Mini Cooper toad.

What you have there is the "hot rod" setup that the regional marine 2-stroke expert recommended to me when I repowered my 4106. I chickened out and opted for 2450 rpm no load, N65s, A timing. This guy has pictures of racing trucks on the wall of his shop, one with quad turbos and 2000 hp! He could talk all day about how he built hundreds of 8V71NAs with N70 injectors, stock cam timing, for the local truckers. He claims that setup gave the best balance between fuel economy and power vs smoke.

Do you know what the cam timing is?

I imagine he knows what he's doing. He has 40 plus years building 2 strokes, nothing else, so he says! I believe him, I've seen his shop!

Mark

EDIT! Oooh! The HOT setup is what you have now and adding propane injection! According to this guy the truckers would head up the hills, the 8V71s setup like you have would start to smoke, then they switch on the propane and the smoke is GONE....... and that little 8V71 would rocket up the hills! I could retell his stories all night. Truthfully, he was a bit disappointed I went with N65s.... lol

There are options other than repower. A low boost turbo, I think sometimes called a smoke turbo, will give some extra power and increase efficiency (no smoke) at altitude and would not require any internal changes. Propane injection could also help.

The N-70's in a coach engine which is fairly common are not too bad about smoke with the right blower, most are set with a 1.496 or a 1.500 gauge if you want the full 318 hp you need to get down and dirty then they do smoke you are probably around 300 hp about the same as a N65 a timed engine

Very slightly when pulling a long grade high up. If you have a rear view mirror that allows such, just watch the smoke; then slowly lift your throttle foot. Or....have somebody follow you with a CB and tell you when the smoke clears.

FWIW, we used to run N70 injectors in stock 353N and 453N DD engines way back in the day. Did not smoke, as the formentioned technique was employed. Our old fire apparatus had N90 injectors in the 671N and 8V71N engines.

The trannys were Fuller T905B models and I do not remember any smoggy smoke, unless we were in the wrong gear or were lugging, which was a big no no from the master mechanic. You have a fine setup. 2500 OK shifting. HB

What timing pin is it set to ? 1.460 , With "A"setting, I liked th 1.470-1.474, found the 1.484 was too far, yup, stuck top ribgs in the piston grooves. But it ran soo sweet & clean.Lot of fun playing these toys.Dave M

I thought the lower timing setting, 1.460 vs 1.484 for example, the 1.460 was more advanced and would burn cleaner. And hotter. Not so? I'm basing this idea on the timing setting instructions in the manual - for N65, for example, it calls for 1.484 with advanced timing or 1.460 with standard timing.

Have played many games on these babes, 6-71, 8V-71 & 12V-71, Both as NA & T & TA versions, Did a fairly wild 6-71 Turbo (wild) pulling tractor at 3600 rpm, more than 1.484 advance etc, why I still prefer the 71 series. Never blew/ scattered one. Have used many injectors from the 65's thru the 140-150's, the 9200 work great in the 92. Lot of smoke both exhaust and tires. Been a great experience.BTDTDave M

Bevans6,You are correct on the timing pins, I must be getting older than I thought, I was trying to time it at the 1.460 but burnt the top of the pistons, then wound up with the 1.474 as the 1.484 was way too average !,, So sorry for getting off track, see it was a good thing I hung up the DDC timing kit etc, before I screwed up too many.Getting old is better than the other possibility I guess. ThanksDave M

I had the same problem with standard timing N65 injectors. Since I have the two piece pistons with tight transit rings, Don Fairchild turbocharged the engine. I added a custom air to air intercooler. Don added the Series 60 12.7 liter turbo with waste gate to keep the boost down to around 15psi since we're still using the high compression pistons and 7G75 injectors. I had the largest radiator made-but on over 90 degree days, have to use misters on hill pulls.The performance is truly different. Went from pulling the Grapevine (6% grade) at 32mph to 45mph with no smoke. I get an initial puff of black smoke, then the turbo takes over and no smoke at any altitude. Highly recommend turboing the 8V-71-REALLY wakes it up. Good Luck, TomC

When doing my tune up I found the injectors were set to a 1.460 pin and that's what I've reset them to. Now with a fresh tune and verified full throttle in my racks and governor I am getting black smoke at sea level.

I'm thinking about going to a 1.484 pin, this is what Ossie w/ Hillsboro Diesel recommended with N70 injectors. What do you guys think?